The problem with feeding the foal only hay or natural pasture is that both are deficient in essential nutrients for proper growth and development. Crucial minerals such as zinc, copper, calcium and phosphorus are usually deficient or out of balance in these forage foods. Quality protein sources are also necessary for the foal to grow up healthy, so if the foal's diet is based only on pasture/hay, the protein levels will also be compromised and lysine, the limiting amino acid, will be in deficit.
Providing a specific concentrated feed for the growth phase of the foals, in conjunction with good pasture and/or hay, is therefore essential to ensure their correct development.